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Wednesday, February 22, 2012

New Type of Alien Planet Is a Steamy 'Waterworld'

NASA, ESA, and D. Aguilar
(Harvard-Smithsonian Center for Astrophysics) - GJ1214b, shown in this artist’s
view, is a super-Earth orbiting a red dwarf star 40 light-years from Earth. New
observations from the …more NASA/ESA
Hubble Space Telescope show that it is a waterworld enshrouded by a thick,
steamy atmosphere. GJ 1214b represents a new type of planet, like nothing seen
in the Solar System or any other planetary system currently known. less

Scientists have discovered a new
type of alien
planet — a steamy waterworld that is larger than Earth but smaller than Uranus.

The standard-bearer for this new class of
exoplanet is called GJ 1214b, which astronomers first
discovered in December 2009. New observations by NASA's Hubble Space Telescope suggest that GJ 1214b is a watery world
enshrouded by a thick, steamy atmosphere.

"GJ 1214b is like no planet we know of,"
study lead author Zachory Berta of the Harvard-Smithsonian
Center for Astrophysics in Cambridge, Mass., said in a statement. "A huge
fraction of its mass is made up of water."

Adding to the diversity

To date, astronomers have discovered more
than 700 planets beyond our solar system, with about 2,300 more "candidates"
awaiting confirmation by follow-up observations.

These alien planets are a diverse bunch. Astronomers have found one
planet as light and airy as Styrofoam, for example, and another as dense as
iron. They've discovered several alien worlds that orbit two suns, like Luke
Skywalker's home planet of Tatooine in the "Star Wars" films. [The
Strangest Alien Planets]

But GJ 1214b, which is located 40
light-years from Earth in the constellation Ophiuchus (The Serpent Bearer), is
something new altogether, researchers said.

This so-called "super-Earth" is about 2.7 times Earth’s diameter and weighs
nearly seven times as much as our home planet. It orbits a red-dwarf star at a
distance of 1.2 million miles (2 million kilometres), giving it an estimated
surface temperature of 446 degrees Fahrenheit (230 degrees Celsius) — too hot to
host life as we know it.

Scientists first reported in 2010 that
GJ 1214b's atmosphere is likely composed primarily of
water, but their findings were not definitive. Berta and his team used Hubble's
Wide Field Camera 3 to help dispel the doubts.

Hubble watched as GJ 1214b crossed in front of its host star, and the
scientists were able to determine the composition of the planet's atmosphere
based on how it filtered the starlight.

"We’re using Hubble to measure the infrared
color of sunset on this world," Berta said. "The Hubble measurements really tip
the balance in favor of a steamy atmosphere."

Berta and his colleagues report their
results online in the Astrophysical Journal.

A watery world

Since astronomers know GJ 1241b's mass and
size, they're able to calculate its density, which turns out to be just 2 grams
per cubic centimeter (g/cc). Earth's density is 5.5 g/cc, while that of water is
1 g/cc.

GJ 1214b thus appears to have much more
water than Earth does, and much less rock. The alien planet's interior structure
is likely quite different from that of our world.

"The high temperatures and high pressures
would form exotic materials like 'hot ice' or 'superfluid water,' substances
that are completely alien to our everyday experience," Berta said.

GJ 1214b probably formed farther out from
its star, where water ice was plentiful, and then migrated in to its current
location long ago. In the process, it would have experienced more Earth-like
temperatures, but how long this benign phase lasted is unknown, researchers
said.

Because GJ 1214b is so close to Earth, it's
a prime candidate for study by future instruments. NASA's James Webb Space Telescope, which is slated to launch in 2018,
may be able to get an even better look at the planet's atmosphere, researchers
said.